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Updating the Honey Locust information from Tree Crops by J. Russell Smith

 
Michael Cox
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Location: Kent, UK - Zone 8
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This thread on honeylocust complements the main book discussion/review thread for Tree Crops. I have tried to reflect both the original authors intentions/enthusiasm for this crop but also update it with the current state of affairs.

J. Russell Smith was very enthusiastic about the use of honeylocust as a fodder crop for livestock. It is thought to be nitrogen fixing (more on this to follow), the pods contain a sweet pulp which is enjoyed by both people and animals, the seeds can be ground to make a high protein meal and the pods fall from the trees in late autumn to early winter nicely supplementing declining forage yields from pasture. Smith points out in the book the huge natural variation between individual plants in terms of size, vigour, thorniness, pod size and sugar content and determines that these honeylocust have huge potential to be improved for fodder potential given an adequate survey for good parent stock and a suitable breeding program over a number of years. For example natural variation in sugar content runs from 15% to over 30% (compared with maple sap which has 3% to 6%) and could likely be bred higher still. Likewise pods could be bred for greater proportions of pulp to seed/shell and there is some suggestion that the pods could be bred to have the seeds in a narrow margin so as to be easily removed with a single knife cut.

Smith's text generally is based on anecdotes collected from contemporary farmers concerning yields, as opposed to strict scientific analysis of yields so his quoted figures should be taken with a pinch of salt.

Nitrogen Fixing of Honeylocust - a non-nodulating leguminous tree

Honey Locust Research Group - Newsletter 2

Regarding nitrogen fixation in leguminous trees, the conventional wisdom has been to divide the family into nodule-forming and non-nodulating species, and to assume that those species without nodules do not fix nitrogen.

This conventional wisdom has now been challenged by Jim Bryan in his 1995 doctoral dissertation for the Department of Forestry at Yale University. Bryan has found evidence that non-nodulating leguminous species apparently do form a symbiotic relation with soil bacteria (Bradyrhizobium spp. or Rhizobium spp.). This endosymbiosis is carried out directly in the roots of the trees rather than in nodules. Honeylocust (Gleditsia triacanthos L.) was the primary species used in Bryan's investigation.

To establish the presence and activity of rhizobial bacteria in the roots of honeylocust, Bryan utilized three techniques: light microscope with stained root slides, scanning electron microscope (SEM), and acetylene reduction. Each technique indicated the possible presence or activity of the rhizobial bacteria inside the honeylocust root cells. The electron micrographs of the rhizobial bacteria in honeylocust roots are impressive. Using the SEM, Bryan also found evidence of bacterial symbiosis in other non-nodulating legume species.

Bryan emphasizes that his research strongly supports, but does not prove, the non-nodule nitrogen fixation. He is continuing his investigation with acetylene reduction of honeylocust seedlings grown under more exacting conditions (in sand and hydroponically), and is also observing other non-nodulating legumes with the SEM.

Interestingly, Bryan initiated his study from an agroforestry perspective. He began by cataloging members of Leguminosae that produce beans (pods) for human consumption. During this cataloging he found that a disproportionate share of the bean producers did not present nitrogen-fixing nodules. He then set out to develop a practical test to identify nitrogen fixing bean producers, and this led him to discover the non-nodule rhizobial symbiosis.

In the approximately 18,000 member Leguminosae family, Bryan found 277 species which produced beans for human consumption. Of the 132 species in this group presently tested, 30% did not present nitrogen fixing nodules, compared with only 11% for the family as a whole. Of the 277 bean producing species, only 9 are native to the temperate zone.
The Gleditsia genus evolved comparatively early within Leguminosae. The nitrogen fixing in honeylocust is in several aspects 'primitive' compared to that found in nodulating legumes. This suggests to Bryan a possible evolutionary continuum within Leguminosae from the non-nodulating species of the Caesalpiniodeae subfamily to the nodulating species.

The implications of Bryan's findings for honeylocust agroforestry are unclear. How much free nitrogen honeylocust will produce, and how much of that nitrogen will be available for grass production is unknown. Almost certainly there will be increased interest in honeylocust. Whether this interest will be justified on the basis of additional free nitrogen will require considerable research.

Bryan, James A. 1995. Leguminous Trees with Edible Beans, with Indications of a Rhizobial Symbiosis in Non-Nodulating Legumes. Doctoral Dissertation, Yale University.
Copies of Jim Bryan's thesis can be obtained from:
University Microfilm International
P.O. Box 1764
Ann Arbor, MI 48106 USA
Telephone: (800) 521-3042
Cost: Microfilm($US32.50);Softcover($US36.50);Hardcover($US43.50)


Development of Locust Varieties since Smith

Sadly the trend in recent years has been to breed away from productive fodder trees and towards ornamental shade trees. The characteristics of a good shade tree are essentially opposite that needed for fodder - specifically a shade tree needs to be "tidy" and not drop fruit and pods, they also tend to be thornless.

Atleast four named fodder varieties were bred and studied and showed marked improvements over the usual locust seedlings.

  • Hershey - the largest and heaviest pods averaging 17 to the lb
  • Calhoun
  • Ashworth
  • Millwood - bred for large pods on a thornless tree(although seen in some places called "milkwood")


  • This development stalled in about the 1940s and now very very few places appear to still grow or produce these for sale, and most are already out of stock until next year. It appears that not all varieties were exported from the USA - Hershey and Calhoun appear to be unobtainable in Europe at present.

    Rolling River Nursery
    Hidden Springs Nursery
    Agroforestry UK - stock Calhoun and Millworth

    These improved Honeylocusts seem to be ideal permaculture crops - high yields of nutritious pods that livestock can self harvest in the field, or that can be collected, dried and stored. Nitrogen fixing. Shade is dappled so only minimally restricts pasture growth beneath.

    Propagation
    These appear to typically be grafted onto young seedling of wild honeylocusts, and there is certainly potential to top work existing honeylocusts in and around farm lands.

    Further development of fodder varieties
    The fact that the existence of these fodder varieties has essentially been forgotten means that development stalled for 60 year and there is plenty of scope for improvement even with fairly small scale breeding programs. Full sized trees take up lots of space, but your could conduct a series of experiments on a single standard tree by topworking the limbs.

  • Conduct a cross breeding between two parents
  • Topgraft young wood from saplings to an established standard tree to encourage early fruiting.
  • Observe developing pods on grafted branches for desirable traits - eg pod size and sugar content
  • Keep best branches as the next generation of parent wood


  • In this way you could take years off successive breeding generations (trees take 6 to 8 years to fruit normally) and only need minimal space - on limb per planted seed.

    Mike
     
    Akiva Silver
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    Great topic, and yes, what a shame that so much focus has been on the sterility of honey locust. What are the pollination requirements of honey locust?, I have always assumed that the non fruiting trees in people's yards are males. Are they dioecious?
     
    Darin Colville
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    Kudzu is an amazing fodder. Only if it's already there. DONT introduce it.
     
    Dan Grubbs
    Posts: 500
    Location: northwest Missouri, USA
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    books chicken dog forest garden goat trees
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    Michael - great stuff.

    Funny, in the middle of my pasture are two massive mulberry tries -- easily 50-feet tall -- remnant of a one-time homestead that stood at the top of the hill and is no longer and left behind only the two trees. Well, under one of these large mulberry trees was this thorny looking stalk thing that I cut down to just above the soil surface but below mower blade. Then, we had our winter and this summer before we cut hay I looked down and saw 6-7 thorny stalks coming from the one I had cut. Well, after a bit of reading here and there, I have discovered it is a honey locust (I hope). And a second tree also sprouting about three feet from the first. I'm going to transplant the small one to the end of one of my swales and the larger bushy one (it's about 3 feet tall now) I will try to foster to a usable forage-producing tree. I was so stoked when I learned what it is and that I'll be able to add one more healthy thing to my goat forage as well as fixing N. I've attached a photo of it so the experts here can give me a positive ID to ensure it's not black locust. It has the large tri-thorns already.

    photo.JPG
    [Thumbnail for photo.JPG]
     
    Michael Cox
    Posts: 1573
    Location: Kent, UK - Zone 8
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    Dan - honey locust definitely has a reputation for sprouting from damaged roots and for forming groves of genetically identical tree by root suckering. You probably have a reasonable nitrogen fixer there, but I'd be looking to top graft it with a THORNLESS and more productive variety if you can get your hands on the. The thorns from a honey locust will go through the sole of a boot, a tractor tire etc...

    Great tree but a bit antisocial!
     
    Kyrt Ryder
    Pie
    Posts: 694
    Location: Graham, Washington [Zone 7b, 47.041 Latitude] 41inches average annual rainfall, cool summer drought
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    Does anybody have a United States source for plants or scionwood for any of the Improved Cultivars?

    Even contact information to someone willing to sell permission to climb and snip scionwood in the winter would be appreciated.

    NOTE: when I say source I mean working source. Several websites claim they are 'out of stock but intend to get more'... and have said the exact same thing for up to five years.
     
    I agree. Here's the link: https://richsoil.com/wood-heat.jsp
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